hey Andrea, don't wanna ruin the plot but...do you think 13 years old is mature enough to play "sleepthrough" and "the corpse in the window" ?
Well, that's a tough question.
I think that (visually and content speaking) a 13 years old boy can be mature enough to play them.
But, maybe (and this is absolutely a personal matter), 13 years aren't enough to have lived through all the experiences that may relate with the games' stories.
The contents (apart from being occasionally scary, spooky and creepy) are pretty safe for you to play, but, as I said, the plot comprehension may not be fully relatable at your age.
In any case, just play them. :)
... but remember: it's strange stuff. ;)